Nonfragmenting field ionization mass spectrometry has been shown recently to be a highly effective method for the quantitative analysis of complex multicomponent mixtures, e.g., urine or plasma extracts. It is proposed to extend the application of this technique by (1) introducing an ion fragmentation chamber at the collector position of the conventional mass spectrometer, followed by an electrostatic mass analyzer, to allow determination of the chemical identity as well as the isomeric and isobaric composition of beams of ions having the same mass number, and (2) substituting the molecular evaporation of the sample by flash evaporation induced by a CO2 laser. This will allow quantitative multicomponent analysis without the necessity for repeated multiple mass scanning and spectrum integration; it would shorten the analysis time from minutes to seconds and would allow the operation of an automatic sample changer. These two components are expected to make the field ionization mass spectrometric system a highly useful tool for routine analysis in the clinical laboratory.